My request is that you find the person who did the blackmailing. I am not asking you to break any laws to do it. This is a sad story, and i know that there are those here who have the ability to find this guy. Unless he's very good at hiding his online presence. Once you find him i suggest you report him to authorities. You can do this creatively, but again try and keep it legal.

Not from 4chan, and not requesting for any death threats. Wasn't aware of the 4chan vigilante human flesh search engine. I requested non-vigilante assistance for the girl who killed herself due to depression.

There are good people in law enforcement who are capable of conducting an investigation of this sort. What's more they have powers to gather ISP logs and other information with a warrant to discover the identity of the culprit.

This is a sad tale but taking upon yourself (or expecting it from another) to investigate this type of incident may be counter-productive and potentially harmful. If evidence is tampered with e.g. unauthorised access to a mail account then the proper judicial process can be put at risk. Legal questions such as what laws have been broken arise and there's often not a good, tested answer at this time.

I share your feelings but this is not a road I suggest we go down. The only exception to this would be in the case of investigative journalism or a privately contracted investigator. Both should be aware of the law and how to conduct an investigation with a view to handing it over to law enforcement if need be.